1. Field of the Invention
The present invention relates to a technique for evaluating whether a speech sound has been aurally comprehended or not. More specifically, the present invention relates to a speech sound intelligibility assessment system for evaluating the degree of “fitting” of a hearing aid or the like to provide a sound of appropriate loudness for each individual user by adjusting the amount of amplification of sounds with respect to each frequency. “Intelligibility” is sometimes referred to as “discrimination score”.
2. Description of the Related Art
In recent years, people suffering from presbycusis are increasing in number due to the aging society. Moreover, due to increased opportunities for listening to loud music for long hours as well as other influences, there is an increasing number of people suffering from hypacusia associated with acoustic traumas.
Moreover, due to the downsizing and improved performance of hearing aids, users feel less of a psychological barrier against wearing hearing aids. Thus, there is an increasing number of users who use hearing aids in order to improve conversational listening comprehension in daily life.
A hearing aid is a device for compensating for the deteriorated hearing of a user by amplifying sounds of frequencies which are difficult for the user to hear. The amount of sound amplification which a user desires in a hearing aid varies depending on the level of deterioration in the hearing of the user. Therefore, before beginning use of a hearing aid, “fitting” is required for adjusting the amount of sound amplification in accordance with the hearing of each user.
Fitting is performed in such a manner that the output sound pressure level of a hearing aid is at an MCL (most comfortable level: a sound pressure level that is comfortable to a user) for each frequency. Problems may occur if fitting is not appropriately done. For example, if the amount of amplification is insufficient, sounds may not be sufficiently heard; or if the amplification is excessive, the user may feel that it is too loud.
Fitting is generally performed based on each user's audiogram. An “audiogram” is a result of evaluating how a pure tone is “heard”: for example, a diagram in which, for each of a number of sounds of different frequencies (e.g., 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz), the smallest sound pressure level (decibel value) that the user can hear is plotted against frequency.
In order to perform fitting, it is necessary to generate an audiogram for each user first. Then, the generated audiogram is subjected to a fitting method, which is a mathematical function for estimating an MCL for each user.
Currently, however, there is no one established fitting method that can determine an optimum amount of sound amplification with respect to any and every user for improving the conversational listening comprehension intelligibility from his or her audiogram alone. Possible reasons are, for example: an audiogram is not in one-to-one correspondence with a conversational listening comprehension ability; a person suffering from hypacusia has a narrow range of sound pressure that is felt to him or her as an appropriate loudness; and a plurality of fitting methods are diversely present.
Therefore, in order to evaluate the degree of fitting, a speech sound intelligibility assessment is needed. A “speech sound intelligibility assessment” is an assessment as to whether a speech sound has actually been aurally comprehend or not, and is an assessment of listening comprehension ability as to whether a monosyllabic speech sound has been aurally comprehend or not. A monosyllabic speech sound means either a single vowel or a combination of a consonant and a vowel (e.g., (a)”/(da)”/(shi)”). Since the purpose of wearing a hearing aid is aural distinction in conversations, assessment results of speech sound intelligibility are regarded as important.
Conventionally, speech sound intelligibility assessment has been performed through the following procedure. First, by using the 57S list (50 monosyllables) or the 67S list (20 monosyllables) proposed by the Japan Audiological Society, a user is allowed to hear a monosyllabic audio via oral presentation or CD reproduction. Next, through oral explanation, writing, or other methods, the user is asked to answer which speech sound he or she has aurally comprehended the presented speech sound to be. Then, an evaluator matches the answers against the list in order to calculate a correctness rate.
However, in the aforementioned assessment method, the user is required to make answers via oral explanation or writing, and the evaluator needs to determine the correctness of the user's answers through manual labor. Thus, this test presents a large burden, and is time-consuming, on the part of the user and the evaluator.
Therefore, for example, Japanese Laid-Open Patent Publication No. 9-038069 discloses a speech sound intelligibility assessment method which, in order to reduce the burden of the evaluator, employs a personal computer (PC) to automatically perform correctness determination. Specifically, Japanese Laid-Open Patent Publication No. 9-038069 proposes a method in which monosyllabic audios are presented to a user by using a PC; the user is asked to answer by using a mouse or via pen-touch technique; the answers are received as inputs to the PC; and correctness determinations as to the presented audios and answer inputs are automatically made. Since answer inputs are received by using a mouse or via pen-touch technique, there is no need for the evaluator to analyze and distinguish the user's answers (which are given by oral explanation or writing), whereby the trouble of the evaluator is greatly reduced.
Moreover, for example, Japanese Laid-Open Patent Publication No. 6-114038 discloses a speech sound intelligibility assessment method in which, after audio presentation, possible choices of speech sounds are presented in the form of text characters, thus reducing the user's burden of making answer inputs. In Japanese Laid-Open Patent Publication No. 6-114038, choices are limited to only a small number so that the relevant speech sound can be found among the small number of characters, whereby the user's trouble of finding the character is reduced. Also in Japanese Laid-Open Patent Publication No. 6-114038, a PC is used to receive answer inputs, thus reducing the evaluator's burden.
However, in the speech sound intelligibility assessment methods described in Japanese Laid-Open Patent Publication Nos. 9-038069 and 6-114038, the user needs to make answer inputs. Therefore, an answer-inputting operation still exists, thus presenting a burden on the user. In particular, it is presumably not easy for people suffering from hypacusia or elderly people who are unaccustomed to working on a PC to make answer inputs by using a mouse or a touch pen. There has also been a possibility that the wrong monosyllable matrix may be inadvertently selected through a manipulation mistake, in which case the speech sound intelligibility may not be correctly evaluated.